1. Field of the Invention
The present invention relates to an electrical connecting member for allowing the electrical connection between electric circuit components such as printed boards in a secure manner, a connecting method for the electric circuit components using that connecting member, and an apparatus therefore.
2. Related Background Art
The methods for obtaining the electrical connecting state between electric circuit components include a wire bonding method, an automatic bonding method based on a tape carrier method as disclosed in Japanese Patent Application Laid-Open No. 59-139636, and a so-called TAB (Tape Automated Bonding) method.
However, these methods had the difficulty that they were all expensive, there were a number of connecting components between electric circuit components, and it was not possible to cope with a high density of electrical joints.
Also, there was a problem that the connecting state could not be obtained collectively between a number of joints, resulting in requiring considerable time for connecting operation and a limited reduction of the cost.
To resolve these difficulties, there is known a method for the electrical connection between electric circuit components in which, for example, electrical joints are formed on a printed board slightly projected from the surface of the printed board, and both electrical joints are bonded together under pressure directly or indirectly with the interposition of a conductive member as the electrical connecting member between both electrical joints, so that the electric circuit components which are printed boards can be electrically connected.
Among the connecting methods for such electric circuit components, is the method shown in FIG. 24. FIG. 24 is a half-size view illustrating a conventional connecting form between electric circuit components, in which 21, 22 are long size substrates which are electric circuit components such as printed boards, and 23, 24 are pressing members. Each substrate 21, 22 of electric circuit component has printed wiring disposed on its surface, or electrical joints 21a, 22a located closer to one side, arranged in parallel, and in the vicinity of the arrangement of electrical joints 21a, 22a, there are provided holes 21b, 22b for passing pressure bonding screws 25 therethrough, both substrates 21, 22 are joined one on the other in the state in which the electrical joints 21a, 22a and holes 21b, 22b are opposed to each other, so as to be interposed between the pressing members 23, 24.
Each pressing member 23, 24 is formed of a metallic plate having a respective thickness, with a screw hole 23a formed on the pressing member 23, and a hole 24a formed on the pressing member 24, respectively, and further the pressing member 24 is formed with a pressing section 24b slightly bent toward the substrate 2 on a portion opposed to the electrical joints 21a, 22a for the connection so as to apply the pressure to the substrates 21, 22 in a secure manner, so that the electrical joints 21a, 22a are bonded with each other by inserting the pressure bonding screws 25 through the holes 24a of the pressing member 24 and the holes 21b, 22b of the substrates 21, 22, threadingly engaging and tightening them into threaded holes 23a of the presser member 23.
On the other hand, in order to improve the connecting state between circuit components, there is also known a method in which electric circuit components are electrically connected, using an electrical connecting member having a plurality of conductive members in an insulating carrier member, in the mutually insulating state.
The manufacturing method for such an electrical connecting member has been proposed in, for example, Japanese Patent Application Laid-Open No. 63-222437, Japanese Patent Application Laid-Open No. 63-228726, Japanese Patent Application Laid-Open No. 63-246835, and Japanese Patent Application Laid-Open No. 2-49385.
One of such electrical connecting members has been proposed in Japanese Patent Application Laid-Open No. 2-49385. In the following, this art will be described with reference to FIGS. 25A and 25B.
FIGS. 25A and 25B shows a conventional electrical connecting member and the connected state of substrates such as printed boards by the use of that member, and FIGS. 25A and 25B are explanation views for illustrating the forms before and after the connection of electrical connecting member, respectively. In the figure, 1 is an electrical connecting member, and 4, 5 are substrates such as printed boards which are electrical circuit boards to be connected. The electrical connecting member 1 is constituted in such a manner that holes are bored into a film-like carrier 2 made of an electrical insulating member, spaced at predetermined intervals, and a plurality of conductive members 3 are provided within the holes in the mutually insulating state. One end of each conductive member 3 is exposed on one face of the carrier 2, and the other end is exposed on the other face of the carrier 2, in the form of slightly projecting from the surface of the carrier 2, the diameter of each end portion being slightly larger than that of the hole to prevent the member from getting out of the hole.
The dimension of each portion in the electrical connecting member 1 is such that the thickness of the carrier 2 is about 10 .mu.m, the diameter of the hole (column portion of conductive member) is about 20 .mu.m, the pitch between holes is about 40 .mu.m, and the amount of projection of the conductive member 3 is about several .mu.m on both front and back faces, as shown in FIG. 25A.
Note that the conductive members 3 are made of a metal having an excellent conductivity, which may be often gold (Au) or gold alloy. The interval between conductive members 3 can be determined under the condition in which the insulating property is assured between adjacent conductive members 3.
The connecting form of the electric circuit component with this electrical connecting member 41 is shown FIG. 25B. In FIG 25A figure 4, 5 are electric circuit components to be connected, and when they are connected using the electrical connecting member 1, the electric circuit components 4, 5 are laid on both faces of the carrier 2, the electrodes 6, 7 for use as the connecting ends are aligned with each other in a plan view, and then these electric circuit components are pressurized and bonded by appropriate means against exposed ends of conductive members 3 on respective opposed faces. Thereby, the electrodes 6, 7, i.e., the electric circuit components 4, 5 are electrically connected via the conductive member 3.
In this connection, it is possible to cope with the increase in the number of joints by disposing densely the conductive members 3 on the face of carrier 2, so that the electrical connection between electrodes 6, 7 is made via a plurality of conductive members 3, as shown. Since these conductive members are of short size, there is the effect that the electrical resistance at the connecting portion can be maintained quite small, with a decreased heating due to the conduction of the current, and a small floating capacitance thereof contributes to the reduction of delay time, whereby the difficulty with the conventional connecting method such as the wire bonding method or TAB method can be overcome.
As the method for joining the electric circuit components using the electrical connecting member more securely, a thermocompression bonding method is well known.
FIG. 26 is a typical view illustrating the thermocompression method and its apparatus for connecting the printed boards with each other, on a partially enlarged scale, in which 4, 5 are substrates such as printed boards which are electric circuit components, 1 is an electrical connecting member interposed between both substrates 4, 5, and 50 is a press.
As clearly seen from FIG. 27, the substrates 4, 5 have the printed wirings applied on one face (or both faces), electrical joints 6, 7 being collectively arranged at positions closer to one side, and the electrical connecting member 1 is formed in such a manner that a plurality of holes 3b bored into the carrier 2 made of an electrical insulating material are filled with conductive members made of gold, each one end of which is exposed to one face of the carrier and the other end thereof is exposed to the other face of the carrier, in the form of being slightly protruded from the surface of the carrier, as shown in FIG. 27.
The electrical connecting member 1 is sandwiched and joined between substrates 4, 5, with the electrical joints 7 of the substrate 5 being opposed to one ends of the conductive members 3 provided on the electrical connecting member 1, and the electrical joints 6 of the substrate 4 being opposed to the other ends of the conductive members 3, and then disposed in this state between the upper and lower halves 51, 52 containing heaters in the press 50.
The upper and lower halves 51, 52 each are secured to pressurizing portions P on a base board B with the interposition of heat insulating members 53, 54, respectively, the electrical joints 6, 7 of the substrates 4, 5 and the conductive members 3 of the electrical connecting member 1 are heated up to a temperature of 350 to 400.degree. C. and pressed under a predetermined pressure.
The electrical joints 6, 7 of the substrates 4, 5 and the conductive members 3 of the electrical connecting member 11 are bonded together under pressure in the heated state to be electrically connected with each other in an alloyed state due to the solid phase metal diffusion.
By the way, such a thermocompression bonding process is shown in detail in FIGS. 28A-28D. FIGS. 28A-28D illustrate a typical cross-sectional view showing the process of bonding compressively the electrical connecting member 1 sandwiched between the substrates 4, 5. First, as shown in FIG. 28A, the electrical joints 6, 7 of the substrates 4, 5 are placed into contact with the conductive members 3 of the electrical connecting member 1 carried therebetween from both face sides, and if the substrates 4, 5 are pressurized, the carrier 2 between adjacent conductive members 3 starts to bulge in the upper and lower directions, due to the deformation of each conductive member 3, particularly with the increasing diameter of column portion located within the carrier 2 (FIG. 28B), then making contact with the surfaces of the substrates 4, 5 if further pressurized (FIG. 28C), and finally the conductive members 3 and the carrier 2 fill a gap between the substrates 4, 5 (FIG. 28D).
FIG. 29 is a graph showing the relation between the amount of deformation of the conductive member and the pressure against the substrate 4, 5 in the above-mentioned process, with the amount of deformation in the axis of abscissas and the pressure in the axis of ordinates. As will be clear from this graph, the pressure may suffice to be small in a process in which the conductive member mainly deforms as shown in FIG. 28B, and if the carrier 2 is placed into contact with the substrates 4, 5 and starts to be deformed, the pressure starts to increase abruptly, and at a state as shown in FIG. 28D, the deformation does not rise even if the pressure is increased.
However, with the connecting method for the electric circuit components as shown in FIG. 24, there is the problem that the electric circuit components 21, 22 are wide and long, and there are a great number of electrical joints to be connected, in which if the density becomes high, it is necessary to increase the number of pressure bonding screws 25 for applying a uniform pressure to each electrical joint but if the number of pressure bonding screws 25 increases, the number of holes 21b, 22b for passing respective screws must be increased correspondingly, so that the wiring patterns are restricted, and if the density of electrical joints is further increased, it is difficult to secure a space for providing the holes 21b, 22b.
Also, when the electric circuit components are electrically connected using the electrical connecting member, if the amount of deformation in the bump of the electrical connecting member is small, a proper force is not exerted between the conductive members of the electrical connecting member and the electrical joints of the substrate, so that the metallic solid phase diffused junction is not securely made, producing the so-called non-compression bonding, as shown in FIG. 28A. This is remarkable when there is a dispersion in the height of conductive members or substrate joints.
When the electric circuit components are thermally bonded under pressure using the electrical connecting member, and using an apparatus as shown in FIGS. 26 and 27, there is the problem that it is difficult to adjust the upper and lower halves 51, 52 of the press 50 to be completely in parallel under the heating condition with the heater, and to bond the substrates 4, 5 and the electrical connecting member 1 compressively with a uniform pressure, due to the occurrence of warpage of the upper and lower halves 51, 52 and the substrates 4, 5, resulting in many failures in the compression bonding and a low yield.
To provide the measure against it, a method and apparatus has been proposed in which the electrical joints 6, 7 of each substrate 4, 5 and the conductive members 3 of the electrical connecting member 1 are individually bonded compressively one for each time, but there is the problem that if the number of electrical joints 6, 7 and conductive members 3 exceeds for example 1000, the operational efficiency will decrease.
Further, in the connection with the electrical connecting member 1, it is necessary to realize the metallic junction state between the electrodes 6, 7 of the electric circuit components 4, 5 and the conductive members 3, but as these contact surfaces are not generally clean, and are covered with oxidized or contaminated layers, it is necessary to apply the pressure to destroy the oxidized and contaminated layers and permit the contact with a new generating face, when pressing the electrodes 6, 7 against the conductive members 3.
Therefore, it is necessary to make the diffused junction between the conductive members of electrical connecting member and the electrodes of electrical circuit component, as shown in FIG. 24 previously described, in the compression bonding with a compression bonding apparatus, or the heating under pressure.
However, in the former, when the electric circuit components to be connected are weak against the pressure, a damage may be caused. On the other hand, in the latter method, as the necessary pressure is small, there is no fear that the electric circuit component may be damaged due to the pressure, and the connecting operation is facilitated, but for a good diffused junction state, the heating up to 200 to 350.degree. C. is required, so that the electric circuit member inferior in the heat resistance such as a plate may be damaged due to the heating.